At present the consensus is that superoxide radicals have both beneficial and deleterious effects upon the living cell. The superoxide radical and its "active oxygen" derivatives have been found to be by-products of pollutants (ozone and high energy ionizing radiation), or certain toxic compounds (paraquat), and are intermediates in a number of biochemical reactions. The oxidative attack of such agents upon biochemical systems can lead to many ill effects, among others, structural damage to biological membranes and disfunction of the living cell. Many of the currently proposed mechanisms on the interaction of superoxide radicals with biological systems are in conflict on whether the immediate reactive species is actually the O2, or its suggested disproportionation product 102 (singlet molecular oxygen), or its reaction product with hydrogen peroxide, the hydroxyl radical generated in the Haber-Weiss reaction. We have studied some reactions of superoxide radicals by the accurate and convenient techniques of pulse radiolysis and continuous-flow and stopped-flow radiolysis/photolysis. We propose to combine thhe techniques of radiation chemistry, photochemistry and biochemistry to carry out the following research: (a) Studied of the properties of superoxide-metal cation complexes and their reactivity with compounds of biological interest. (b) Study of the metal catalyzed Haber-Weiss reaction. (c) Studies on singlet molecular oxygen. (d) Studies of hypoxanthine-, xanthine- and uric acid free radicals by pulse radiolysis. (e) Studies of the effect of "active oxygen" species on biological membranes. All reactions will be investigated on a quantitative basis with complete product analysis, essential for mechanism studies.